The present invention relates to a suspension strut or damper for a motor vehicle in which the suspension strut can be gas charged. The present invention also provides a method of gas charging such a suspension strut, and a seal for such a suspension strut. Gas charged suspension struts can provide improved ride quality for the motor vehicle.
Known arrangements of suspension strut comprise a tube which is closed at one end and which defines a fluid chamber, a piston rod extending through the other end of the tube, and a seal providing a substantially fluid tight seal at the other end of tube between the tube and the piston rod. For gas chargeable suspension struts, the seal typically comprises an outer lip which engages the piston rod, an inner lip which engages the piston rod, and a channel portion between the inner and outer lips. The outer lip acts as to substantially prevent dirt and other contaminants reaching the fluid chamber. The inner lip acts to substantially prevent fluid and/or gas leaving the fluid chamber. In order to gas charge the suspension strut, pressurised gas is introduced directly into the channel portion as the outer lip prevents gas entering the fluid chamber. The pressurised gas in the channel portion forces the inner lip away from the piston rod to allow gas to enter the fluid chamber. The inner lip effectively acts as a one-way valve. Several methods for gas charging are known, most of which include the steps of moving the piston rod relative to the tube until a shoulder, groove, or channel in the piston rod aligns with the channel portion in the seal to provide a passage between the channel portion and a position outside the tube, introducing pressurised gas to the passage and hence into the fluid chamber, and then moving the piston rod to close the passage. All of these arrangements, most of which are disclosed in GB Patent Application No. 2,099,956A, require accurate machining of the piston rod to provide the shoulder, groove, or channel. Other arrangements include using a special tool which engages and moves the outer lip. These arrangements can damage the outer lip and ruin its sealing operation.